Characterization of neo-centromeres in marker chromosomes lacking detectable alpha-satellite DNA

Abstract

Recent studies have implicated alpha-satellite DNA as an integral part of the centromere, important for the normal segregation of human chromosomes. To explore the relationship between the normal functioning centromere and alpha-satellite DNA, we have studied eight accessory marker chromosomes in which fluorescence in-situ hybridization could detect neither pancentromeric nor chromosome-specific alpha-satellite DNA. These accessory marker chromosomes were present in the majority of or all cells analyzed and appeared mitotically stable, thereby indicating the presence of a functional centromere. FISH analysis with both chromosome-specific libraries and single-copy YACs, together with microsatellite DNA studies, allowed unequivocal identification of both the origin and structure of these chromosomes. All but one of the marker chromosomes were linear mirror image duplications, and they were present along with either two additional normal chromosomes or with one normal and one deleted chromosome. Indirect immunofluorescence analysis revealed that the centromere protein CENP-B was not present on these markers; however, both CENP-C and CENP-E were present at a position defining a 'neo-centromere'. These studies provide insight into a newly defined class of marker chromosomes that lack detectable alpha-satellite DNA. At least for such marker chromosomes, alpha-satellite DNA at levels detectable by FISH appears unnecessary for chromosome segregation or for the association of CENP-C and CENP-E at a functional centromere.

Partial tetrasomy 12pter-12p12.3 in a girl with Pallister-Killian syndrome: extraordinary finding of an analphoid, inverted duplicated marker

“…Due to their mitotic stability, it was proposed that these analphoid markers contained neocentromeres, a region of chromatin that may act as a functional centromere. 12 The mechanism of formation of the marker chromosome in our patient appears to be similar to that of two cases published by Depinet et al 13 The analphoid marker 12p is of paternal origin; reduction of paternal heterozygosity to homozygosity in all analysed STRs indicates a postzygotic mitotic error. Summarising the so far published data on the mechanism of formation of analphoid, inverted duplicated markers, postzygotic mitosis as cell stage of origin has been described three times, while maternal or paternal meiotic errors could each be delineated only once.…”

“…In 50% of GTG-banded metaphases a supernumerary marker chromosome was found {karyotype: 47,XX,15p+,+mar [13]/46,XX,15p+ [13]}.The marker showed a primary constriction and resembled in size and shape an acrocentric chromosome of the G-group (Figure 2A). A whole chromosome 12 painting probe stained the marker chromosome completely.…”

Epigenetic engineering: histone H3K9 acetylation is compatible with kinetochore structure and function

“…Independent of this sequence preference, specific deposition of the centromeric histone H3 variant CENP-A (Earnshaw and Rothfield, 1985) is thought to form the basis for an 'epigenetic' maintenance of centromere identity (Allshire and Karpen, 2008;Okamoto et al, 2007;Vafa and Sullivan, 1997;Warburton et al, 1997). The epigenetic control of centromere activity is strikingly illustrated by the inactivation of centromeres on dicentric chromosomes (Earnshaw and Migeon, 1985;Earnshaw et al, 1989;Merry et al, 1985;Sugata et al, 2000;Sullivan and Schwartz, 1995) and by rare neocentromeres that recruit CENP-A and assemble fully functional kinetochore structures on non-alphoid DNA (Alonso et al, 2007;Depinet et al, 1997;du Sart et al, 1997;Saffery et al, 2000;Warburton et al, 1997).…”

Tetrasomy 15q26: a distinct syndrome or Shprintzen-Goldberg syndrome phenocopy?

“…There have been at least 13 previously reported cases of tetrasomy 15q in the form of a marker chromosome. 10,11,15,[20][21][22][23][24][25][26][27][28][29] However, in only 10 of the 13 are specific clinical data available ( Table 1) with 9 of the 10 reported as mosaic tetrasomy 15q. Nonetheless, the craniofacial gestalt observed in all our cases is also present in eight of eight cases tetrasomic for 15q25 where clinical images are available ( Table 1).…”